1. Field of the Invention
The invention relates to a process for re-transmitting single frequency signals, of the type used in a single frequency signal repeater and comprising the steps of: [a] receiving a first radio frequency signal through a receiving antenna, the first radio frequency signal having a receiving power, [b] optionally, converting the first radio frequency signal into a process signal, [c] filtering the signal, [d] amplifying the signal, [e] automatically controlling the signal gain, [f] reconversion, as the case may be, of the process signal into a second radio frequency signal, [g] amplifying the power of the second radio frequency signal, [h] output filtering the second radio frequency signal, and [i] transmitting the second radio frequency signal through a transmitting antenna, where coupling takes place between the transmitting antenna and the receiving antenna. The invention also relates to a single frequency signal repeater, of the type comprising: [a] a receiving antenna, for receiving a first radio frequency signal, having a receiving power, [b] a base unit, for converting, optionally, the first radio frequency signal into a process signal, filtering the signal, amplifying the signal, automatically controlling the signal gain, and reconverting, as the case may be, the process signal into a second radio frequency signal, [c] a power amplifier unit, [d] an output filter, and [e] a transmitting antenna, where the transmitting antenna and the receiving antenna may undergo coupling.
2. Related Art
The present invention relates, therefore, to signal processing, and the corresponding device therefor, the repeater, to be incorporated in DVB (Digital Video Broadcasting), DAB (Digital Audio Broadcasting), GSM, etc. repeaters that transmit in the same channel as they receive, whereby they operate in single frequency. This invention allows these repeaters to have high gains, so that for one same received signal level its transmitted power is increased and, consequently, its coverage area is increased. The ultimate aim of the system is to be able to cover the same area of service with a smaller number of repeaters, thereby reducing costs.
The main limitation of the repeaters that operate in single frequency resides in the fact that the reception and transmission frequency of the repeater is the same, whereby a certain degree of coupling exists between the transmitting and receiving antennas, that is to say, the receiving antenna receives an echo of the transmitted signal. This can cause the repeater to oscillate. Also, said coupling distorts the signal frequency. In accordance with the state of the art, an effective way of avoiding this, or of reducing it to insignificant values, is achieved by reducing the repeater's gain. However, a consequence of this is that the area of coverage thereof is also reduced.
An attempt has been made in the repeaters used so far to alleviate this problem by means of, for example, the use of reduced coupling transmitting and receiving antennas. However, this solution is expensive and not very satisfactory, since is not possible to avoid the coupling completely. By way of example, let us consider the case in which the transmitted signal is reflected from an object close to the repeater (a tree, a car, etc.). The echo caused by the reflection from said object will introduce a coupling between antennas not contemplated at the time of designing their radiation diagrams, whereby it will not be possible to avoid it.